I may be too late with my comment, but if I'm not, you ''Definitely'' need some type of tab or bolt on the pipe that will be in the concrete. If you don't have access to a welder, you could drill holes straight through the pipe & put a length of threaded rod through the pipe. I'd do it in a couple of places & maybe at a right angle to each other. Use nuts to tighten the rods to the pipe & maybe put some large washers (maybe fender washers) on the ends of the rods & hold them in place with nuts. The rods only need to extend a 3 or 4 inches beyond the external wall of the pipe. As far as the size of the rods, I wouldn't use anything smaller than 1/2in. threaded rod. I've lost count of how many dishes I'd put in or repaired self-installed dishes. If the homeowner (the self-installer) didn't weld at least a 4 to 6in. long X 2in. wide piece of 1/4in. thick steel plate to the pipe around a foot or so from the bottom of the pipe, it'll turn in the concrete. Occasionally we'd use factory made poles in an install & that's about the size of the tab & the location it was welded on them. To be honest, the 2 threaded rod setup might be better if you're putting the dish up in an area that's liable to catch a lot of wind.